Uncertainty Analysis and Experimental Validation of Identifying the Governing Equation of an Oscillator Using Sparse Regression

In recent years, the rapid growth of computing technology has enabled identifying mathematical models for vibration systems using measurement data instead of domain knowledge. Within this category, the method Sparse Identification of Nonlinear Dynamical Systems (SINDy) shows potential for interpretable identification. Therefore, in this work, a procedure of system identification based on the SINDy framework is developed and validated on a single-mass oscillator. To estimate the parameters in the SINDy model, two sparse regression methods are discussed. Compared with the Least Squares method with Sequential Threshold (LSST), which is the original estimation method from SINDy, the Least Squares method Post-LASSO (LSPL) shows better performance in numerical Monte Carlo Simulations (MCSs) of a single-mass oscillator in terms of sparseness, convergence, identified eigenfrequency, and coefficient of determination. Furthermore, the developed method SINDy-LSPL was successfully implemented with real measurement data of a single-mass oscillator with known theoretical parameters. The identified parameters using a sweep signal as excitation are more consistent and accurate than those identified using impulse excitation. In both cases, there exists a dependency of the identified parameter on the excitation amplitude that should be investigated in further research.

A Perturbation Approach for Lateral Excited Vibrations of a Beam-like Viscoelastic Microstructure Using the Nonlocal Theory

In this paper, we investigate the lateral vibration of fully clamped beam-like microstructures subjected to an external transverse harmonic excitation. Eringen’s nonlocal theory is applied, and the viscoelasticity of materials is considered. Hence, the small-scale effect and viscoelastic properties are adopted in the higher-order mathematical model. The classical stress and classical bending moments in mechanics of materials are unavailable when modeling a microstructure, and, accordingly, they are substituted for the corresponding effective nonlocal quantities proposed in the nonlocal stress theory. Owing to an axial elongation, the nonlinear partial differential equation that governs the lateral motion of beam-like viscoelastic microstructures is derived using a geometric, kinematical, and dynamic analysis. In the next step, the ordinary differential equations are obtained, and the time-dependent lateral displacement is determined via a perturbation method. The effects of external excitation amplitude on excited vibration are presented, and the relations between the nonlocal parameter, viscoelastic damping, detuning parameter, and the forced amplitude are discussed. Some dynamic phenomena in the excited vibration are revealed, and these have reference significance to the dynamic design and optimization of beam-like viscoelastic microstructures.

Vergleichende Untersuchung der Verschleißbilder von Steckverbindern aus Reibverschleiß- und Vibrationsprüfungen mit unterschiedlichen Prüfrichtungen

In this study a comparison between the wear patterns of electrical connectors resulting from two different test types, namely fretting corrosion test and vibration test, is conducted. In both tests, the excitation directions include the mating direction as well as the orthogonal directions corresponding to the mating direction. Different measurement techniques are used to identify similarities and differences between the wear resulting from these test types. The results show fundamentally different critical directions with regard to wear for the respective test types. Furthermore, it is shown that the induced movement of the fretting tests lead to a higher degree of wear than the vibration tests. Also, it is not adequately possible to establish a direct relationship between the induced movement and the excitation amplitude caused by the attached wires since there is a superposition of several movements in the case of real applications.

Competitive Failure of Bolt Loosening and Fatigue under Different Preloads

Existing research on the competitive failure relationship, failure mechanism, and influencing factors of bolt loosening and fatigue under different preloads is insufficient. This study analyzes the competitive failure relationship between bolt loosening and fatigue under composite excitation through competitive failure tests of bolt loosening and fatigue under different preloads. The results indicated that the failure mode of the bolt is only related to the load ratio (R) and is unrelated to the initial preload and excitation amplitude, which only determine the failure life of the bolt. The small axial loads of composite excitation can restrain bolt failure, and the significant degree of this restraining effect is different for different preloads. Subsequently, a fracture analysis of the bolt was performed to verify the competitive failure relationship of the bolt from a microscopic perspective, and the competitive failure mechanism of the bolt was determined. Based on the findings, we propose a calculation equation for the optimal preload of 8.8 grade high-strength bolts that can serve as a reference for engineering applications.

Analysis of Nonlinear Cyclically Symmetric Isolation Sistem of a Cargo in a Container under Plane Harmonic Vibrations

The problem of calculating the system of a cylindrical shaped load transverse damping installed in a coaxial container is considered. This system has several annular belts of insulation with a cyclically symmetric arrangement of shock absorbers along the circumferential direction. A simple dynamic model of one insulation belt formed by polyurethane tunnel-type shock absorbers is investigated. Such shock absorbers have a high energy absorption coefficient and can operate at very high drafts comparable to their height, which is important when the space between the cargo and the container wall is limited. Within the proposed model framework, a harmonic nonlinear analysis of cargo plane oscillations under kinematic excitation coming from the container is considered. A method for reducing a nonlinear cyclically symmetric system with discrete elastic elements, which allows limiting the analysis to the calculation of a vibration isolation system with one degree of freedom, is proposed. Using the harmonic linearization procedure, the amplitude-frequency characteristics of oscillations and plots of vibration isolation coefficients of cargo at different values of excitation amplitude have been obtained. The results are verified by comparing the analytical solution with the results of numerical integration for a non-reduced nonlinear system with two degrees of freedom. The obtained solution allows choosing the vibration isolation belt parameters, in particular the number of shock absorbers and their stiffness, depending on the conditions of kinematic excitation and permissible overload

Multiwave Total Focusing Method for Full-Matrix Imaging Using Ultrasonic Phased Array

The imaging range of the traditional total focusing method (TFM) is usually limited by the directivity of excitation of a single wave pattern. In this paper, a multiwave TFM technique is proposed, which uses both compression and shear vertical (SV) waves for detection and imaging simultaneously. Based on this technique, a special ultrasonic transducer for multiwave detection is designed that can balance the excitation amplitude of compression and SV waves. Multiwave TFM uses the compression and SV wave fields generated by the same excitation, and the signals reflected by the two sound fields passing through the discontinuity are received. The signals are respectively processed by TFM according to the compression and SV wave velocities. The two processed signals are shifted and aligned according to the time difference between the compression wave with SV wave propagation, and then added together. Finally, the detection image of the block is obtained. Through simulation and experiments, it is shown that the special transducer can optimize the imaging range and effect of multiwave TFM, and multiwave TFM can effectively detect discontinuities and reduce the rate of missed detection at higher steering angles. The detection results show that the maximum amplitude gain of multiwave TFM relative to TFM can be increased about 6 dB.

Research on a high power density mechanical-electrical-hydraulic regenerative suspension system for high-speed tracked vehicles

High power density energy regeneration is one of the effective solutions to solve the contradiction between improving the damping performance and energy consumption of active suspension. The hydraulic commutator is used to realize hydraulic rectification and hydraulic variable speed/pump/motor with few teeth difference gear pairs is used to match the speed, combined with permanent magnet motor power generation and power supply to put forward kilowatt level high power density mechanical-electrical-hydraulic regenerative suspension system for high-speed tracked vehicles. The mathematical model and fluid-solid-thermo-magnetic multiphysics coupling model are built to analyze the damping performance and regenerative characteristics of the system under passive and semi-active working conditions. The simulation results show that the damping force of the system increases with the increase of the road excitation amplitude and the semi-active control can be realized by adjusting the duty cycle with the PWM control rectifier module. The high power density mechanical-electrical-hydraulic regenerative suspension system can realize kilowatt level energy regeneration, and the regenerative efficiency is more than 50% under low-frequency excitation. The temperature rise of the system is low during operation, which is helpful to improve the reliability and service life.

Dynamic modeling and damping performance improvement of two stage ISD suspension system

In this paper, the dynamics of the vehicle suspension system under the random excitation and the periodic excitation are investigated. To improve the damping performance of the vehicle suspension system, a two stage ISD suspension with “Inerter-Spring-Damper” in each stage is proposed based on electromechanical similarity theory. A vehicle dynamic model with two stage ISD suspension is established in this paper. The dynamic equation is solved by the Runge-Kutta method and the dynamic response of the whole vehicle system is obtained. Taking the traditional suspension as the comparison object, the dynamic characteristics of the system under random excitation and periodic excitation are studied in the time domain, and the suppression effect of the suspension designed in this paper on the resonance peak is verified in the frequency domain. The influence of the inertia coefficient on the damping performance of the vehicle suspension system is analyzed. The effects of excitation amplitude and vehicle speed on ride comfort improvement of vehicle system with two stage ISD suspension are discussed respectively. The results show that, the resonance peak values of body acceleration, dynamic travel of rear suspension and rear tire dynamic load frequency response are reduced by 59.1%, 21.6%, and 60.3% respectively. With the increase of excitation amplitude in the range of 0.02–0.04 m, the ride comfort improvement of two stage ISD suspension system is always more than 61%. With the increase of vehicle speed in the range of 10–25m/s, the performance improvement rate of two stage ISD suspension system can reach more than 34.1%.

Mode coupling internal resonance characteristics of submerged floating tunnel tether

This study presents the mode coupling internal resonance characteristics of submerged floating tunnel tether. In which, in-plane and out-of-plane coupling of tether is taken into account. And the coupled vibration equations of tether for the in-plane first mode and out-of-plane first mode are obtained. The one-to-one mode coupling internal resonance characteristics of submerged floating tunnel tether are studied by numerical analysis method. It is shown that, when the conditions of modal coupling internal resonance are met, with the increase of the external excitation amplitude of the tether, the mid-span displacement of the tether increases gradually. When the amplitude of external excitation is less than a certain value, the internal resonance of tether will not occur. With the increase of damping ratio, the mid-span displacement of the tether decreases gradually. When the damping ratio increases to a certain value, the internal resonance will not occur. The study is helpful to restrain the vibration of submerged floating tunnel tether.

Sidelobe level minimization for uniform circular smart antenna array using cultural algorithm

Cultural algorithm (CA) is a new evolutionary program inspired by sociology and archaeology theories that assisting formulating cultural evaluation. Its use to solve optimization problems. This paper analyzed the beamforming of a uniform circular antenna array (UCAA) via using the CA algorithm. The sidelobe level (SLL) is minimized by adjusting the appropriate weight for each element. In addition, the optimal beam pattern is achieved by using CA for UCAA, which means that the main beam is steering to the desired user, while the nulls represent the interference signals. The excitation amplitude is supposed to be constant while the elements are assumed isotropic. The circular array number elements and the interspacing distance between them are setting as optimization parameters. The simulation results show that the CA rationally reacts to the changing environments, and it is valuable for SLL reduction. A −25 dB of relative SLL is achieved under beam scanning (0º) and (15º), respectively.